Image Number 7 for United States Patent #4662796.
The invention relates to a travelling support pillar for use in underground mines.The support pillar has a link subjected to the action of a positioning jack. The positioning jack extends between a gate and the rear of the top of the pillar. The positioning jack hydraulically locks the support pillar by means of a sliding pressure-relief valve to compensate for load changes due to the movement of the floor or the roof. The link also permits the support pillar to be collapsed for transportation, and it provides a support pillar with a shorter length and a lower height in the collapsed position, and it permits the top of the support pillar to be placed closer to the working face of the mine when the pillar is in its roof supporting extended position.